Patent GB-1050421-A (GB)
Abstract: 1,050,421. Acoustic well logging. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. Feb. 24, 1964 [Feb. 25, 1963], No. 7619/64. Headings H4D. An acoustic well logging tool comprises, Fig. 1, a plurality of transmitting transducers 13, 14 and 15 each of which is formed from a cylindrical shaped section 51, Fig. 3 (not shown), of magnetostrictive material, e.g. barium titanate, with a coil 52 disposed thereon, each transducer generating an acoustical impulse when a current is passed through the coil, a single receiver 16, formed, Fig. 2 (not shown), of a slab of piezo-electric material 42, and a link member 50, on which the transducers and receiver are mounted along a common axis in a spaced relationship, the transducers being mounted all on one side of the receiver. The supply to the transmitter transducers may be by means of conductors 53 lying in a spiral groove on the surface of the link member 50. The link member 50 may comprise a rubber tube surrounding a stress absorbing chain 54 having electrically insulating portions to render it non- conductive. The receiver may comprise a stack of piezo-electric tourmaline discs having a resonant period that is shorter than the time interval between the arrivals at the receiver of the compressional waves and the shear waves produced by the transmitters, and mounted on a conductor 41 and housed in a flexible plastic boot 43 filled with silicon grease or oil and with a block of Neoprene 40 forming the base. The plastic boot 43 &c. are housed in turn in a container comprising upper and lower heads 30 and 31 joined by a plurality of circularly spaced tubes 32, the bores of the tubes forming passages for the cables connected to the transmitter transducers &c. Plugs 33 are provided for external electrical connections. The above ground equipment may comprise an oscilloscope 22 displaying the output of the receiver and a camera 25 for photographing the resulting trace. A programming device 21 controls the energizing of the transmitters. A selsyn device 23 coupled to the cable lowering the logging tool is connected to the oscilloscope circuitry 20 so that an indication of the tool's depth may be given on the oscilloscope. The use of a plurality of transmitting transducers and a single receiver, as against the normal vice versa arrangement, is said to overcome interference in cable 12 between the outputs of the plurality of receivers. It is also stated that later arriving acoustical waves, e.g. shear waves, may be recorded as against the early arriving compressional waves. A method of determining the quantity where Vs and V L  are the shear wave and compressional wave velocities respectively of the bore hole material, is described, based on measurements taken off displaced tracer, Fig. 4A and Fig. 4B (both not shown), resulting from transmissions from transmitters 13 and 14 and by use of the equation where T<SP>1</SP>22 and T<SP>1</SP>12 are the times of reception of the first shear wave pulse and the first compressional wave pulse respectively, shown in Fig. 4A, and T<SP>1</SP>21 and T<SP>1</SP>11 are the corresponding shear and compression times shown in Fig. 4N, and S1 and S2 are the respective spacings between the receiver 16 and each of the transmitters 13 and 14. A method of identifying the first shear wave pulse in the traces by further such measurements is also described by determining the first pulse which follows the preceding pulse by a period different in the two traces Figs. 4A and 4B.